Summary The authors present the results of the investigations which have been made in Chile on Chagas' disease to December 31, 1947. In systematic epidemiological surveys made upon representative samples of the zones infected by the endemic, 12,581 persons have been examined, of whom 12 per cent revealed infestation by T. cruzi. The human cases proven parasitologically, reached 1,631 cases, distributed from Tarapacá to O'Higgins. A total of 8,142 Machado-Guerreiro reactions have been made, with 17 per cent positive. A total of 4,006 domestic and wild animals have been examined, which showed 10 per cent positive on xenodiagnosis. Of 20, 614 examples of T. infestans collected in diverse zones of the country, 44.4 per cent were found to be infected by T. cruzi. The profilaxis of Chagas' disease was undertaken by means of the application of DDT on a large scale in the rural zones; the treatment of 830 houses with 5 per cent DDT in kerosene showed that the multiplication of triatomids was controlled in 90 per cent of the cases, the indices remaining low up to twelve months after the application. Authors believe that DDT is not the ideal insecticide against triatomids. Benzene hexachloride is more promising.